Method and device for the sensor reduced regulation of a permanent magnet excited synchronous machine

ABSTRACT

A method and a device for providing field-oriented regulation of a synchronous machine excited by a permanent magnet, in which a direct-axis voltage component and a quadrature-axis voltage component of the control voltage for the synchronous machine are determined from a quadrature-axis current component setpoint value thus determined and from rotational speed information using a stationary machine model in a decoupling network. These voltage components are converted into triggering pulses for the synchronous machine. The regulating system does not require any information regarding the phase currents of the polyphase system.

FIELD OF THE INVENTION

The present invention relates to a method and device for providingsensor-reduced regulation of a synchronous machine excited by apermanent magnet.

BACKGROUND INFORMATION

It is already understood in automotive engineering that a synchronousmachine excited by a permanent magnet (PM synchronous machine) may beinstalled in the drive train of a vehicle as an integrated crankshaftstarter generator between the internal combustion engine and thetransmission.

Such a PM synchronous machine is regulated in the rotor-field-orientedcoordinate system. FIG. 1 shows an example of field-oriented currentregulation of a PM synchronous machine having a pulse-width-modulationinverter. This is based on an actual value measurement of the phasecurrents of a three-phase system and determination of a direct-axiscomponent and a quadrature-axis component of the regulating voltage withrespect to the rotor position, based on actual measured values. Thequadrature-axis component of current is proportional to the desiredtorque.

With this regulation, phase currents ia, ib, ic derived from thethree-phase system of the PM machine are converted in a Park transformer13 into Id_actual and Iq_actual currents of a rectangular coordinatesystem. Current Id_actual is the actual value for the direct-axiscomponent of current of the machine. Current Iq_actual denotes theactual value for the quadrature-axis component of current of themachine.

Actual value Id_actual of the direct-axis current component is sent viaa heterodyne element 12 to a direct-axis current component regulator 1,and actual value Iq_actual of the quadrature-axis current component issent as the actual value to a quadrature-axis current componentregulator 2. Heterodyne element 12 receives as another input signal afeedback signal which is obtained from output quantity uq′ of astationary decoupling network 5. In addition to achieving the decouplingwhich is important for the regulating effect, stationary decouplingnetwork 5 also fulfills the function of achieving field weakening ondirect-axis current component regulator 1 in the upper rotational speedrange in conjunction with output limiters 3 and 4 and an anti-windupmethod. This field weakening of the PM synchronous machine at higherrotational speeds is necessary because otherwise the induced machinevoltage would be greater than the maximum power converter outputvoltage. The latter is limited by the power supply voltage, i.e., thevehicle electrical system voltage. In this field weakening operation,the power converter is operated in an override state, so the powerconverter output voltage is no longer sinusoidal.

The setpoint input of direct-axis current component regulator 1 receivesa setpoint signal generated by a direct-axis current component setpointgenerator 9 and the setpoint input of quadrature-axis current componentregulator 2 receives a setpoint signal generated by a quadrature-axiscurrent component setpoint generator 14. Quadrature-axis currentcomponent setpoint generator 14 generates the quadrature-axis currentcomponent setpoint signal as a function of the output signal of abattery voltage sensor.

At the output of direct-axis current component regulator 1, amanipulated variable Id* for the direct-axis current component is madeavailable, and at the output of the quadrature-axis current componentregulator 2 a manipulated variable Iq* is made available for thequadrature-axis current component. These manipulated variables are sentto stationary decoupling network 5 which determines a direct-axisvoltage component ud′ and a quadrature-axis voltage component uq′ forthe regulating voltage of the PM synchronous machine using themanipulated variables mentioned above.

These regulated voltage components ud′ and uq′ which are regulatedvoltage components in the rectangular coordinate system, are sent viaoutput limiters 3 or 4 to an inverse Park transformer 6, which has thefunction of converting regulated voltage components ud and uq which arelimited in the rectangular coordinate system to regulated voltagecomponents ua, ub and uc of the three-phase system. These are convertedin a pulse inverter 7 into triggering pulses for PM synchronous machine8.

Quadrature-axis voltage component uq′ of the regulated voltage output atthe output of stationary decoupling network 5 is sent to absolute valuegenerator 10, which determines absolute value |uq′| of thequadrature-axis voltage component.

The output signal of absolute value generator 10 is used as the inputsignal for a threshold value switch 11. If absolute value |uq′| exceedsa predetermined threshold value, then the value 0 is output at theoutput of threshold value switch 11. If absolute value |uq′| falls belowthe predetermined threshold value, then the value 1 is output at theoutput of threshold value switch 11.

Exemplary embodiments of a decoupling network in which a stationarymachine model is stored are discussed and described in German patentdocument no. 100 44 181.5 by the present applicant

German patent document no. 100 23 908 discusses a method for determiningthe rotor position of an electric machine which may be, for example, athree-phase generator having a pulse-width-modulation inverter, with arotor winding, a stator equipped with inductors and a voltage sourcesituated between two phase terminals also being provided. In thismethod, using switching elements provides for branching into two phasesin which the particular phase voltage characteristics are measured.Superimposing them permits an unambiguous determination of the rotorposition. In the case of this method, the rotor positions for eachvoltage curve are stored in the form of tables.

In addition, the journal ETEP, Vol. 8, No. 3, May/June 1998, pp. 157-166discusses a permanent-magnet synchronous machine having field-weakeningoperation in which there is a large ratio of maximum speed to basicspeed. This is achieved by an additional negative D component of thestator current. As part of the regulation of an available synchronousmachine, the rotor position is measured using the output signals ofthree Hall sensors, one Hall sensor being assigned to each phase U, Vand W.

SUMMARY OF THE INVENTION

The exemplary embodiment and/or exemplary method of the presentinvention provides a sensor-reduced regulating system which does notrequire any current sensors or current measurement. Only the batteryactual voltage and the rotor angle or angular position are measured,rotational speed information also being derived from the latter bydifferentiation of the position information over time.

In generator operation of the PM synchronous machine, there is nosacrifice of performance in comparison with conventional field-orientedregulating systems.

Since PM synchronous machines may be used as crankshaft startergenerators and are used there in the sense of a high-currentapplication, the elimination of the need for current sensors is of greatadvantage because the required current sensors in high-currentapplications are particularly complex.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a prior art field-oriented currentregulation for a PM synchronous machine.

FIG. 2 shows a block diagram of an exemplary method of a field-orientedcurrent regulation according to the present invention for a PMsynchronous machine.

FIG. 3 shows a diagram illustrating the fundamental mode frequency ofthe current as a function of rotational speed.

FIG. 4 shows a diagram illustrating the maximum phase-angle error as afunction of rotational speed.

DETAILED DESCRIPTION

FIG. 2 shows a block diagram of an exemplary embodiment of afield-oriented current regulation according to the exemplary embodimentand/or exemplary method of the present invention for a PM synchronousmachine 8. In this regulating method, it is not necessary to derivephase currents from the polyphase system of the PM machine and convertthem into the actual value of the direct-axis current component and theactual value of the quadrature-axis current component of a rectangularcoordinate system by using a Park transformer.

The device shown in FIG. 2 has a logic unit 18 which supplies a setpointvalue Iq_setpoint for the quadrature-axis current component at itsoutput. In addition, logic unit 18 has a plurality of inputs. A firstinput of logic unit 18 is connected to a higher-level control unit 14. Asecond input of logic unit 18 is connected to the output of a batteryvoltage regulator 17. The third input of logic unit 18 receivesinformation regarding rotational speed n of the machine.

Battery voltage regulator 17 is connected at the input to a batteryvoltage setpoint generator 15 and a battery voltage sensor 16. Batteryvoltage setpoint generator 15, e.g., a higher-level energy managementsystem supplies battery setpoint voltage U_(BS) to battery voltageregulator 17. Battery voltage senor 16 is provided for measuring batteryactual voltage U_(BI). The battery actual voltage is picked up at anintermediate circuit capacitor (not shown), for example.

The starting procedure is as follows: a start command comes fromhigher-level control unit 14 and contains information regarding setpointtorque M_setpoint. In logic unit 18 quadrature-axis current componentsetpoint value Iq_setpoint is derived from this value. Quadrature-axiscurrent component setpoint value Iq_setpoint is sent to stationarydecoupling network 19 which contains a stationary machine model. In thisdecoupling network the quadrature-axis current component setpoint valueis converted to a direct-axis voltage component ud and a quadrature-axisvoltage component uq of the regulating voltage by including rotationalspeed n and the stored machine model. A stored table which takes intoaccount machine parameters is used for this purpose. Depending on theaccuracy of the machine model, more or less great sacrifices inperformance occur with this conversion.

Beyond a predetermined rotational speed threshold value, e.g., 500 rpm,reversing logic 18 performs a reversing operation on the basis of whichoutput signal I_(DC) _(—) setpoint of battery voltage regulator 17 isnow relayed as quadrature-axis current component setpoint valueIq_setpoint to decoupling network 19. In this network thequadrature-axis current component setpoint value is converted into adirect-axis voltage component ud and a quadrature-axis voltage componentuq of the regulating voltage by including rotational speed n. This alsomakes use of the stored table in which machine parameters are taken intoaccount. Inaccuracies in the machine model are compensated by thehigher-level voltage regulation and do not result in any loss ofefficiency in generator operation.

Voltage components ud and uq, which are determined via the stationarymachine model and which are regulating voltage components in therectangular coordinate system, are sent to an inverse Park transformer6. This has the function of converting regulating voltage components udand uq in the rectangular coordinate system into regulating voltagecomponents ua, ub and uc of the three-phase system, taking into accountrotor angle γ, which is determined by a position sensor 24. Thesevoltage components are sent to a pulse-width-modulation inverter 7 whichat its output provides triggering pulses for PM synchronous machine 8.The output of pulse-width-modulation inverter 7 is connected via areversing unit 23 to PM machine 8 which is to be controlled.

Voltage components ud and uq are also sent to a computing unit 20 whichdetermines from these voltage components setpoint angle

between the rotor pole axis and the setpoint stator voltage vector. Thefollowing equation is used for this purpose:

$\varepsilon = {\arctan\mspace{11mu}{\frac{ud}{uq}.}}$

In the field-oriented regulation, zero-frequency quantities areregulated with a time constant that is the same over the entireregulating range, so computing unit 20 operates with the same clockfrequency as the regulation.

The output signal of computing unit 20 is sent to a block switchmechanism 21 which is cycled directly by rotor angle γ. Informationregarding the rotor angle is obtained via a position sensor 24, forexample—as already explained above. Block switch mechanism 21, whoseoutput signal is also sent to reversing logic 23, is used to selecttriggering pulses according to one of six possible switch states of thepower converter.

Instead of a block switch mechanism, a software program whichcorresponds functionally to the block switch mechanism may also be used.

In reversing logic 23 there is a reversing operation in the sense thateither the triggering pulses generated in pulse-width-modulationinverter 7 or those generated in block switch mechanism 21 are forwardedto PM machine 8. This reversing operation is performed as a function ofrotational speed n taking into account an adjustable switchinghysteresis implemented by hysteresis circuit 22. The hysteresis range isbetween 800 and 1000 rpm, for example.

Such triggering ensures a smooth transition from pulse-width-modulationinverter operation, in which the output signals of circuit block 7 aresent via reversing logic 23 to PM machine 8, to block operation, inwhich the output signals of block switch mechanism 21 are sent viareversing logic 23 to PM machine 8. This is attributed to the fact thatthe same regulator structure is used for the entire rotational speedrange and at the reversing rpm the output signal of block switchmechanism 21 is equal to the output signal of pulse-width-modulationinverter 7, with the output signal of pulse-width-modulation inverter 7being subject to a statistical angle inaccuracy, i.e., a jitter, whichincreases with an increase in rotational speed and results in unwantedfluctuations in power in the upper rotational speed range.

The transition from pulse-width-modulation inverter operation to blockoperation as described above is performed in order to avoid theseunwanted power fluctuations in the upper rotational speed range.

These power fluctuations in the upper rotational speed range which occurin the related art are based on the fact that the switching frequency ofthe pulse-width-modulation inverter, i.e., the PWM inverter, must not beselected to be too great from the standpoint of the losses occurring.For the case of an application in a crankshaft starter generator, a PWMfrequency of 8 kHz is therefore used, for example. The relationshipbetween the rotational speed and the fundamental mode frequency of thecurrent is therefore as follows:

$f = {\frac{n}{60} \cdot {p.}}$

For the rotational speed range of a 2·p=24-pole crankshaft startergenerator whose rotational speed range is between 0 and 6500 rpm, afrequency range of 0 to 1300 Hertz is therefore necessary. This is shownin FIG. 3, which is a diagram illustrating the fundamental modefrequency of the current as a function of the rotational speed. Thisdiagram shows rotational speed n in rpm on the abscissa and frequency fin Hertz on the ordinate.

A PWM frequency of 8 kHz prevails over the entire operating range, sothis yields an angle inaccuracy with respect to the setpoint voltagezero crossing and the voltage zero crossing actually switched due to theratio of the fundamental mode of the current to the pulse frequency.This is depicted in FIG. 4 which shows a diagram illustrating themaximum phase-angle error based on the setpoint voltage zero crossing asa function of the rotational speed for a PWM frequency of 8 kHz. Thisdiagram shows rotational speed n in rpm on the abscissa and phase-angleerror WF in degrees on the ordinate.

The statistical inaccuracy, i.e., jitter, results in unwanted powerfluctuations in the upper rotational speed range. To prevent thisstatistical inaccuracy, an rpm-dependent switching, i.e., anrpm-dependent transition from PWM operation to block operation occursaccording to the exemplary embodiment above described on the basis ofFIG. 2. As an alternative, the power fluctuations mentioned above mayalso be prevented by increasing the PWM frequencies, e.g., to switchingfrequencies up to 90 kHz. However, this is not advisable because of thehigh switching losses and high power converter complexity.

Other advantages of the exemplary embodiment depicted in FIG. 2 includethe fact that there is only a slight additional processor load becausecomputing unit 20 is able to operate at a constant regulating frequencyindependently of the rotational speed. In the case of PWM operation overthe entire regulating range, the PWM frequency and thus the frequencyfor the inverse Park transformation would have to be increased with therotational speed, which would have resulted in a great processor load.

In addition, the switching frequency of the power converter is low,which is associated with low switching losses of the power converter.

Furthermore, the angle inaccuracies attributable to PWM cycling areeliminated and thus the unwanted power fluctuations attributable to themare also eliminated. The angle inaccuracy depends only on the positionsensor itself.

A list of the Reference Notations is as follows:

-   1 Direct-axis current component regulator-   2 Quadrature-axis current component regulator-   3 Limiter-   4 Limiter-   5 Decoupling network-   6 Inverse Park transformer-   7 Pulse-width-modulation inverter-   8 PM synchronous machine-   9 Direct-axis current component setpoint generator-   10 Absolute value generator-   11 Threshold value switch-   12 Heterodyne element-   13 Park transformer-   14 Higher-level controller (engine control unit)-   15 Battery voltage setpoint generator-   16 Battery voltage sensor-   17 Battery voltage regulator-   18 Logic unit-   19 Decoupling network with a stationary machine model-   20 Computing unit-   21 Block switch mechanism-   22 Hysteresis circuit-   23 Reversing logic-   24 Position sensor for rotor angle-   ia, ib, ic Phase currents from the three-phase system-   Id_actual Actual value of direct-axis current component-   Id_setpoint Setpoint value of direct-axis current component-   Iq_actual Actual value of quadrature-axis current component-   Iq_setpoint Setpoint value of quadrature-axis current component-   Id* Manipulated variable for the direct-axis current component-   I_(DC) _(—) setpoint Quadrature-axis current component setpoint    value of the battery voltage regulator-   Iq* Manipulated variable for the quadrature-axis current component-   M_setpoint Setpoint torque-   n Rotational speed-   ua, ub, uc Regulating voltages for the three-phase system-   U_(BS) Battery voltage setpoint value-   U_(BI) Battery voltage actual value-   ud, ud′ Direct-axis component of the regulated voltage-   uq, uq′ Quadrature-axis component of the regulated-   voltage-   WF Phase-angle error-   Setpoint angle-   γ Rotor angle

1. A method for field-oriented regulating a synchronous machine excitedby a permanent magnet, the method comprising: determining aquadrature-axis current component setpoint value; supplying thequadrature-axis current component setpoint value and rotational speedinformation to a decoupling network which contains a stationary machinemodel; determining a direct-axis voltage component and a quadrature-axisvoltage component in the decoupling network as a function of only thequadrature-axis current component setpoint value, the rotational speedinformation and the stationary machine model; and converting thedirect-axis voltage component and the quadrature-axis voltage componentinto triggering pulses for the synchronous machine.
 2. The method ofclaim 1, wherein the quadrature-axis current component setpoint value isdetermined in a logic unit.
 3. The method of claim 2, wherein areversing operation is performed in the logic unit as a function of apredetermined rotational speed threshold value.
 4. The method of claim3, wherein the quadrature-axis current component setpoint value isderived by a higher-level control unit at rotational speeds which arelower than the predetermined rotational speed threshold value.
 5. Themethod of claim 4, wherein the quadrature-axis current componentsetpoint value is derived from a setpoint torque predetermined by thehigher-level control unit.
 6. The method of claim 5, wherein thesetpoint torque is the starting torque.
 7. The method of claim 3,wherein the quadrature-axis current component setpoint value is derivedby a battery voltage regulator at rotational speeds which are greaterthan the predetermined rotational speed threshold value.
 8. The methodof claim 7, wherein the battery voltage regulator determines thequadrature-axis current component setpoint value as a function of abattery voltage setpoint value supplied by a higher-level energymanagement system and a battery voltage actual value supplied by abattery voltage sensor.
 9. A device for field-oriented regulating asynchronous machine excited by a permanent magnet, comprising: adecoupling network which includes a stationary machine model having aninput for a quadrature-axis current component setpoint value and aninput for rotational speed information, and which is provided fordetermining a direct-axis voltage component and a quadrature-axisvoltage component as a function of only the quadrature-axis currentcomponent setpoint value, the rotational speed information and thestationary machine model, and a conversion unit which is connected tothe decoupling network for converting the direct-axis voltage componentand the quadrature-axis voltage component into triggering pulses for thesynchronous machine.
 10. The device of claim 9, wherein it includes alogic unit having an output for the quadrature-axis current componentsetpoint value.
 11. The device of claim 10, wherein the logic unit hasan input for rotational speed information and for performing a reversingoperation as a function of a predetermined rotational speed thresholdvalue.
 12. The device of claim 11, wherein the logic unit outputs at itsoutput a quadrature-axis current component setpoint value which isderived by a higher-level control unit at rotational speeds which arelower than the predetermined rotational speed threshold value.
 13. Thedevice of claim 12, wherein the logic unit derives the quadrature-axiscurrent component setpoint value from a setpoint torque which is derivedby the higher-level control unit.
 14. The device of claim 13, whereinthe setpoint torque is a starting torque.
 15. The device of claim 11,wherein the logic unit outputs at its output a quadrature-axis currentcomponent setpoint value which is supplied by a battery voltageregulator at rotational speeds which are greater than the predeterminedrotational speed threshold value.
 16. The device of claim 15, whereinthe battery voltage regulator has a battery voltage setpoint value inputwhich is connected to a higher-level energy management system and has abattery voltage actual value input which is connected to a batteryvoltage sensor.